When Theo Chesley got a close look at one of two volcanoes erupting in Alaska he felt awed and a little afraid.

“It looked to me like that mountain was broke right open,” said the pilot who flies regular routes along the Alaska Peninsula and Aleutian Islands, where the Pavlof and Cleveland volcanoes have rumbled to life.

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“You could see the ash coming out of the top … it was lit up like a Roman candle. I mean [at times] there was 300, 400, 500 yards of straight fire coming out of the top, like you’d see in Jurassic Park or something,” he said Monday.

Both volcanoes were relatively quiet, Monday, but the Alaska Volcano Observatory has issued warnings stating that either or both could erupt in the weeks or months ahead, sending ash plumes into the atmosphere and possibly disrupting air traffic between Asia and North America.

Pavlof is located close to the end of the Alaska Peninsula and is one of the most active volcanoes in the region, erupting more than 40 times since the late 1700s. Cleveland is located on Chuginadak Island, in the Aleutian chain, about 640 kilometres farther West, and has had 19 eruptions since 1980.

Neither volcano is close enough to any settlements to pose a threat, but Mr. Chesley said local flights near Pavlof have been grounded four or five times because of concerns about ash clouds, which can damage aircraft engines.

He said it was clear to him the volcano has the potential to push an ash plume high enough into the air to pose a threat to international flights.

“You are 20 miles off and you see a little wisp of smoke then all of a sudden within 15 seconds it would be almost like a mushroom cloud coming out the side of the mountain and it would go up into the atmosphere, just like a big cumulus cloud,” he said. “I mean we were able to deal with it because we are [flying at a] low level and were able to see where the ash was going. But for the people operating at 20,000 feet and above, if there is a cloud layer you couldn’t risk it because you couldn’t see it coming.”

About 20,000 to 30,000 people fly daily between North America and Asia over routes that pass close to the Aleutian Islands. Most international flights are above 30,000 feet.

When the Eyjafjallajokull volcano erupted on Iceland in the spring of 2010 it sent ash plumes high enough to disrupt flights across Europe for several days.

Jeff Freymueller, co-ordinating scientist with the University of Alaska, Fairbanks, said volcano experts are keeping a close watch on Pavlof and Cleveland.

“We are checking every few hours, 24 hours a day, to see if there is any ramping up,” he said.

Dr. Freymueller said Pavlof’s long history shows there have been several big eruptions over time, the latest in 1996 when an ash plume went up more than 30,000 feet, and that could happen again

“Mostly, stay tuned,” he said when asked whether international flights could be disrupted.

Catherine Hickson, an adjunct professor of earth and ocean sciences at the University of British Columbia, said an increase in seismic activity is the best way to tell whether a volcano is headed for a massive eruption.

“It can come suddenly, but generally it ramps up for hour to days beforehand,” she said.

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